Experimental and Numerical Aeroelastic Analysis of Airfoil-Aileron System with Nonlinear Energy Sink

Abstract

Recent studies on nonlinear passive absorbers present high control efficiency for broadband frequency range with low added mass. This work presents a configuration of an airfoil typical section where the flap is considered as a Nonlinear Energy Sink (NES), which adds zero mass and has a cubic stiffness. An aeroelastic test-bench was created and characterized for linear and nonlinear structural configurations and tested in a subsonic wind-tunnel experimental campaign. The strongly nonlinear hardening stiffness is obtained by using linear springs and geometric nonlinearities. For the nonlinear tests, several Limit Cycle Oscillation (LCO) and subcritical and supercritical Hopf bifurcations were observed. Numerical analysis was also carried out for both linear and nonlinear cases using: Unsteady Vortex Lattice Method (UVLM) and Theodorsen theory (both low fidelity), Euler (medium fidelity) and Reynolds-Averaged Navier Stokes (high fidelity) methods. The numerical methods present good agreement, within the limits of each approach, and correspond with the experimental data. Using the NES, a gain of flutter speed is reached compared to the linear flap restoring force configuration.